1. Field of the Invention
The invention relates to a transition between stripline transmission lines that is efficient at microwave frequencies and readily fabricated.
2. Prior Art
In high frequency circuits stripline transmission lines are in common use. The advantage of such circuits is that they may be patterned by an automated photographic process that allows for efficient electrical design. Stripline provides not only efficient high frequency runs from point to point, but many important passive functions such as impedance transformation, delay, filtering, power division or combination, and directional coupling.
A major limitation of stripline occurs when it is desired to effect cross-overs. There are, of course many circuit applications in which cross-overs are required. In an example of practical interest, the cross-over issue is presented in monitoring a four element antenna circuit of a phased array radar system for amplitude and phase. Cost constraints dictate that four antenna drive circuits be placed in a common package with four dipole antennas, four independent signal paths including filters to the four dipole antennas and four monitoring or calibrating paths. The monitoring, which may originate from one point, must in principle, cross at least two of the four antenna signal paths, if each signal path is to be monitored. Cross-over in the antenna stripline circuit is achieved by use of two coaxial transitions from a singly branched monitoring circuit also in stripline, and placed on the main antenna circuit. The two branches of the monitoring circuit enter the stripline of the antenna circuit at two transitions disposed between pairs of antenna paths. The monitoring circuit is then branched a second time on the antenna circuit, and the four branches are then coupled to the four antenna signal paths without further ado.
The transitions at microwave frequencies represent a problem as well as a solution to the cross-over problem. The transition, taking into account the constraints of stripline manufacture, and the small thickness dimensions in which a transition may occur, ordinarily create objectionable mismatches, electrical discontinuities, and parasitic reactances at such transitions. The customary result of these factors is to make transitions less than optimum at microwave frequencies.